No abstract

Obesity, from declining estrogen levels after menopause, increases the risk of heart disease, diabetes, and hypertension. Ovariectomy (OVX) in rats is a good model of estrogen insufficiency. The ensuing mild obesity is useful to study how hypoestrogenism alters adiposity. This study examines the hypothesis that in ovariectomized (OVX) rats modification of estrogen levels or treatment with a selective estrogen receptor modulator, raloxifene (RAL), alters leptinemia and modulates leptin receptor (Ob-R) abundance in hypothalamus and white adipose tissue, similar to the modification of adipose status induced by hypoestrogenism. Mid- and long-term studies (7 and 22 wk) were conducted to monitor the change in leptinemia in rats after estrogen loss by OVX and after estrogen replacement by 17beta-estradiol (OVX+E(2)) or RAL treatment (OVX+RAL). Leptin was significantly higher in OVX rats vs. controls, in a time-dependent manner. This effect was reversed by both E(2) and RAL treatment at 7 wk (P < 0.05) and 22 wk (P < 0.001). Moreover, E(2) or RAL treatment reversed the OVX-induced increases in food intake, body weight, and fat mass content; the modifications of serum parameters were examined to evaluate the different lipid profiles. We also evaluated Ob-R expression in hypothalamus and adipose tissue by Western blot analysis. The expression of the long functional isoform (Ob-Rb) increased at 7 wk only in adipose tissue and decreased at 22 wk in OVX rats in both tissues; these effects were reversed by E(2) or RAL treatment. We provide evidence that central and peripheral Ob-Rb expression is related to modification of estrogen levels.

1 Leptin, a pleiotropic hormone believed to regulate body weight, has recently been associated with in¯ammatory states and immune activity. Here we have studied the e ect of leptin on expression of IFN-g-induced nitric oxide synthase (iNOS) and cyclo-oxygenase-2 (COX-2), both prominent markers of macrophage activation, using the murine macrophage J774A.1 cell line.2 After 24 h of incubation, leptin (1 ± 10 mg ml 71 ) potently synergized with IFN-g (100 U ml 71 ) in nitric oxide (NO) release, evaluated as nitrite and nitrate (NO x ), and prostaglandin E 2 (PGE 2 ) production in culture medium. 3 The observed increase of NO and PGE 2 was related to enhanced expression of the respective inducible enzyme isoforms, measured in mRNA and protein by RT ± PCR and Western blot analysis, respectively. 4 When cells were stimulated only with leptin, a weak induction of NO and PGE 2 release and of the expression of related inducible enzymes was observed. 5 Moreover IFN-g increased the expression of the functional form of leptin receptor (Ob-Rb) and this e ect was potentiated by leptin in a concentration-dependent manner. 6 These data suggest that macrophages, among the peripheral immune cells, represent a target for leptin and con®rm the relevance of this hormone in the pathophysiology of in¯ammation.

The binding of ¹²⁵I-labeled rat prolactin (¹²⁵I-rat PRL) to membranes from different regions of the rat brain was studied. Among these regions the hypothalamus showed the highest specific binding. Clearly detectable specific binding was also observed in substantia nigra, whereas it was very scanty in other brain regions. No significant sex differences in PRL binding to various brain regions were observed, except for hypothalamus where a higher binding was observed in female rats. The binding of ¹²⁵I-rat PRL to hypothalamus from female rats was inhibited in a dose-dependent manner by both unlabeled rat and ovine PRL but not by several other polypeptide hormones. Scatchard analysis of the binding revealed the presence of the binding sites with low capacity and high affinity for rat ligand. Ovariectomy markedly decreased PRL binding in the hypothalamus; an even more pronounced decrease was found after hypophysectomy of female animals. A treatment with estradiol restored the PRL binding in the ovariectomized rats to above normal levels. These results of in vitro biochemical analysis together with the experimental modulation of hormonal status provide strong preliminary evidence for the presence of PRL binding sites in rat brain.

Raloxifene (RAL) is a selective estrogen receptor modulator presenting tissue-specific agonist activity. The aim of this study was to examine whether RAL has an estrogenic effect on carrageenan-induced acute inflammation. Adult female rats were ovariectomized (OVX) 7 wk before edema or pleurisy to deplete circulating estrogens. Edema formation and selected inflammatory markers in inflamed paw tissue were measured in intact (sham-operated) and OVX rats. Groups of OVX rats were treated with RAL (1, 3, or 10 mg/kg) or 17beta-estradiol (E2, 25 microg/kg), and these treatments began 2 d after surgery and continued until carrageenan paw edema or pleurisy. Ovariectomy amplifies the inflammation, and we found that RAL, as well as E2, attenuates inflammation and tissue damage associated with paw edema and pleurisy. In treated rats, there is a decrease in edema development and formation, and in polymorphonuclear cell infiltration and migration, as shown by myeloperoxidase measurement and cell counting. RAL and E2 treatments decrease cyclooxygenase-2 and inducible nitric oxide synthase expression in inflamed areas and counteract the inhibition of peroxisome proliferators-activated receptor-gamma expression caused by ovariectomy, restoring this receptor protein expression to sham-operated levels and identifying a possible peroxisome proliferators-activated receptor-dependent antiinflammatory effect of these drugs. Moreover, RAL and E2 increase cytoprotective heat shock protein 72 expression, which seems to be closely associated with the remission of the inflammatory reaction. In addition, we confirm the antiinflammatory effect of RAL in male rats, using a single administration of RAL or E2.